By DPA, [RxPG] Gaza City, May 18 - After days of intense rocket fire on its southern territory, Israel pushed ahead with an aerial campaign against Hamas in the Gaza Strip Friday killing five Palestinians.

Israeli F-16 warplanes attacked a Hamas building in two pre-dawn strikes half-an-hour apart on the eastern outskirts of Gaza City, near the Karni commercial crossing with Israel, killing five and injuring four.

The dead included four members of Hamas' military wing and a civilian bystander, a spokesman for the Palestinian health ministry's ambulance service confirmed, adding two other Hamas members were in critical condition.

Later in the morning, Israel targeted a group of Hamas gunmen in northern Gaza, just after they had launched a rocket into Israel, but no one was reported injured.

Friday's deaths brought to 12 the number of Palestinians killed in seven air strikes since early Thursday afternoon that included attacks on a Hamas security compound in the heart of Gaza City and on several vehicles.

Two Palestinian children and a bystander were among the dead Thursday when Israeli aircraft hit a garbage truck in the southern Gaza town of Rafah.

Earlier, another Qaasam struck synagogue in Sderot, located some kilometres north-east of the Strip, after midnight, shortly after a visit to the battered Israeli town by Israeli Prime Minister Ehud Olmert.

Since an escalation in the rocket fire Monday night, more than 90 rockets have been launched at southern Israel, about a third of which have hit Sderot, where Israelis have been running to shelters, while several hundred have temporarily evacuated the town.

Hamas' military wing has claimed responsibility for firing most of the rockets and Israel has made it the main target of its air attacks.

Hamas, in turn, has threatened to renew suicide bombings in Israel for the first time in more than two years.

Israel has accused the ruling radical Islamic movement of trying to drag it into the internal Palestinian power-struggle, in order to divert attention away from five days of heavy Hamas-Fatah clashes and funnel the anger of militant factions in Gaza against Israel, rather than each other.

A tense calm prevailed in the Gaza Strip Friday, with no new deaths reported in internal clashes, after five people were killed in persisting clashes throughout the strip Thursday.

Two others had died of wounds, raising to at least 52 the number of people killed in five days of Hamas-Fatah fighting bordering on civil war, that has shaken the foundations of the unity government two rival Palestinian groups formed just two months ago with the primary aim of ending such violence.

A spokesman for the group's armed wing, Abu Obeideh, threatened that Hamas would 'execute' anyone who tried to stop its militiamen from launching the rockets at Israel, Israel Radio reported, after Fatah-dominated security forces - who take their orders from Palestinian President Mahmoud Abbas - deployed in northern Gaza to prevent the launching of rockets.

Hamas denied accusations by a website close to Mohammed Dahlan, an influential Fatah official in Gaza, that its militants had planned a stakeout against the president.

US President George W. Bush, at a joint news conference with British Prime Minister Tony Blair in Washington, said he was 'concerned' about the violence in Gaza, which has shattered a six-month ceasefire, and called on 'the parties to work toward a two-state solution.'

US Secretary of State Condoleezza Rice telephoned both Olmert and Abbas to express US concerns Thursday.

Israeli tanks meanwhile have taken up positions at two points several hundred metres inside the northern Gaza Strip, but a military spokeswoman said they were a small number positioned close to the border fence and not there for 'attack purposes.'